1. Field of the Invention
The present invention relates to a method for handoff in a mobile communication system, and more particularly to a handoff method of allocating the most suitable resource for quality of service (QoS) simultaneously with a handoff according to channel states in a mobile station performing the handoff when the handoff occurs due to movement of the mobile station in a mobile communication system.
2. Description of the Related Art
In general, the radio channel state of a mobile station continuously changes due to the mobility of the mobile station. In order to reflect such a characteristic, a system such as an Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA) system estimates the channel state of a mobile station to allocate a range of resources (such as a specific subcarrier group, a specific time slot, etc.) for providing the best QoS between the corresponding mobile station and a base station.
For example, FIG. 1 is a diagram illustrating a handoff procedure and resource allocation in a sectored system. As shown in FIG. 1, favorable resource ranges ‘FRA’ and ‘FRB’ for mobile station ‘1’ (MS1) in sectors A and B, respectively, are different. FIG. 2 is a diagram illustrating a handoff procedure and resource allocation upon a handoff between cells. When a handoff is performed between cells, a favorable resource range ‘FRS’ in a serving cell and a favorable resource range ‘FRT’ in a target cell are different, similar to the case of the sectored system of FIG. 1.
However, since the resource range allocated as above considers only the channel state between a mobile station and a serving base station to which the mobile station is currently connected, a favorable resource range for a mobile station in a current serving cell may not be a favorable resource range for the mobile station in connection to a neighbor base station other than the current serving cell. Therefore, when a handoff is performed without taking into consideration this situation, resources are allocated without an optimal resource allocation procedure between a mobile station and a target base station to which the mobile station will be connected after the handoff, so that the throughput of a corresponding cell may decrease and the QoS may degrade due to the handoff.
Meanwhile, conventional representative handoff schemes include a network-controlled handoff (NCHO) scheme, a mobile-controlled handoff (MCHO) scheme, a mobile-assisted handoff (MAHO) scheme and a neighbor-assisted handoff scheme. However, these schemes propose only methods for determining if a handoff is performed and controlling loads of serving and target cells according to a handoff, but do not propose a method for adaptively allocating resources according to channel states of a mobile station performing a handoff.